data a;
input a;
cards;
1
2
3
4
10
;
run;
data a;
set a nobs=obs;
call symput('obs',put(obs,best12.));
run;
data a;
set a;
if _n_=&obs. then call symput('last',put(a,best12.));
run;
data a;
set a;
b=a/&last.;
run;

学习了~

正是我想要的。多谢多谢！